1. Field of the Invention
The present invention relates to a semiconductor memory device.
2. Description of the Related Art
Resistance change memory has attracted increased attention as a likely candidate for replacing flash memory. As described herein, it is assumed that the resistance change memory devices include Resistive RAM (ReRAM), in a narrow sense, that uses a transition metal oxide as a recording layer and stores its resistance states in a non-volatile manner, as well as Phase Change RAM (PCRAM) that uses chalcogenide, etc., as a recording layer to utilize the resistance information of crystalline states (conductors) and amorphous states (insulators).
It is known that the variable resistance elements in resistance change memory have two modes of operation. One is to set a high resistance state and a low resistance state by switching the polarity of the applied voltage, which is referred to as “bipolar type”. The other enables the setting of a high resistance state and a low resistance state by controlling the voltage values and the voltage application time, without switching the polarity of the applied voltage, which is referred to as “unipolar type”.
To achieve high-density memory cell arrays, the unipolar type is preferable. This is because that the unipolar type solution enables, without transistors, cell arrays to be configured by superposing variable resistance elements and rectifier elements, such as diodes, on respective intersections between bit lines and word lines. Moreover, large capacity may be achieved without an increase in cell array area by arranging such memory cell arrays laminated in a three-dimensional manner (see, Japanese Unexamined Patent Publication No. (Kohyo) 2002-541613).
In an arrangement of a plurality of laminated crosspoint-type memory cell arrays, selection transistors need to be connected to many word lines and many bit lines. Accordingly, the area occupied by such selection transistors becomes large in a periphery of the memory cell arrays. This is regarded as a problem.